The drilling process creates cuttings at the bit, which must be carried to the surface for drilling to continue efficiently. Conventional methods of hardbanding place a strip of wear resistant material around the entire circumference of a component to protect the major diameter from wear due to contact of the component with the formation, casing or other components. By design, the diameter of a conventional hardband is larger than the component it is placed on. A conventional hardband is applied around the circumference of a tubular component, along the horizontal axis of the component, which is perpendicular to the longitudinal axis of the component (FIG. 1). The increased diameter of the band around the entire circumference of the component protects that component from wear by contact with the formation or casing, however it can become an obstacle for cuttings produced during drilling as they make their way to the surface, carried by drilling fluid.
The presence of an obstacle to cuttings is of particular importance during directional drilling when the drill string can be pulled to the bottom side of the hole by gravity. In the circumstance when the string, a section of the string, or a particular component of the string is pulled to one side of the hole, cuttings can become trapped on the leading edge of a conventional hardband. A narrower than normal gap on one side of the hole will result in a wider gap on the opposite side of the drilling string given a constant hole size. A wider gap would result in preferential mud flow on the wider side, and therefore less effective cuttings removal from the narrow side. The combined effects of less effective mud flow and the obstacle to cuttings passing due to the geometry of the hardband can result in a significantly increased residence time of cuttings in a specific area of the drill string. The specific area is most commonly an area of steel on the downhole side of a hardband, which has minimal resistance to wear and erosion. In certain formations, particularly those with a high sand content, it is possible to have similar wear on the uphole side of a hardband as significant drilling time can be spent back reaming the hole due the presence of loose sand. The erosion of the unprotected steel is compounded by the rotation of the drill string with cuttings trapped or piled up in a specific location.
The effects of wear and erosion caused by cuttings can damage expensive machined components, and damage hardbands by removal of material adjacent to, or underneath the hardband. Removal of substrate steel adjacent to, or underneath a hardband (FIG. 2) results in additional costs to repair the wear surface that protects the major diameter of the component of the drill string it is placed on. In addition, the undermining of the hardband reduces the potential useful life of the component compared with a situation where damage due to wear induced by a relatively high residence time of cuttings in a particular location does not occur.
Exxon Mobile holds U.S. Pat. No. 8,602,113 which is titled “Coated Oil and Gas Well Production Devices”. The associated text states that “[t]he patterned hardbanding design will enable the sand grains to preferentially take an alternate path through the non-contact areas due to the hydrodynamic forces, and avoid a direct path through the maximum pressure of contact”. The text also references the types of patterns shown in the prior art as depicted in FIG. 3 stating that these shapes “can be applied directly or machined in the hardbanding after bulk application” and continues to provide a more specific example where “a non-limiting exemplary design considering this is a single bead spiral made by laser welding techniques”. The single bead laser welded spiral is described as one “wherein the angle is small in reference to the horizontal axis of the hardbanding section, and the grooves or regions between hardbanding material are 1 mm-5 mm deep and 1 mm-5 mm wide”.